Effects of predation depend on successional stage and recruitment rate in shallow benthic assemblages of the Southwestern Atlantic

Abstract

Although predation is broadly considered a key process shaping the structure of marine communities, recent studies reported inconsistent consumer effects on the structure of sessile benthic assemblages, even in subtropical areas where the density and diversity of predators can be high. In a subtropical area of the coast of Brazil, Southwestern Atlantic (23°48′S, 45°22′W), the effect of predators on subtidal benthic assemblages was tested by manipulating consumers access to experimental units. Community attributes were then measured at two different successional stages (30 and 100 days) and two spatial scales (within and among sites a few kilometers apart). Since recruitment can modulate predation, settlement rate and composition of recruits were also estimated at each site. Consumer effects were not general, depending on both site and successional stage. During early succession, and at sites where bare space was promptly occupied, predation did not reduce species richness, probably because settlement of a diverse species pool was intense. However, where recruitment rate was reduced and space occupation slower, predation decreased species richness as has been commonly observed in tropical areas. In later assemblages, and at sites where recruitment was intense, predation altered species composition, either facilitating poorer competitors or mediating competitive interactions between dominant species, as predicted by classical theory for temperate areas. This study shows that the outcome of predation in subtropical areas may vary, with effects either resembling those reported to the tropics or more aligned to classic observations in temperate areas. We advocate that variation between these extremes can be largely explained by recruitment dynamics.